1. Field of Invention
Various embodiments of the present disclosure relate to an optical module, and more particularly, to a low-price subminiature optical module for transmitting a high frequency signal.
2. Description of Related Art
Due to the development of network technologies such as broadband mobile, clouding network, IPTV and smart phone and the like, video-based high-capacity communication is increasing explosively. In line with this increase, the transmission speed of optical modules has also improved significantly. Now, there is a pressing need for a technology that could realize small-sized highly efficient optical modules at low cost.
Generally, in the case of a mini-flat type package of a single channel, DC (Direct Current) and high-speed RF (Radio Frequency) signal wirings are realized using a high price ceramic feed-through and a low price FPCB (Flexible Printed Circuit Board). However, a multi-channel optical module, that is, an optical module with four or more channels has much more pins compared to that with a single channel, and thus when a wiring is realized using one FPCB, there is a problem that the width of the FPCB becomes bigger than that of the metal package of the optical module. Thus, in conventional technologies, in order to resolve this problem, a DC/RF flexible printed circuit board is individually connected to a ceramic feed-through consisting of numerous layers to configure a subminiature optical module.
However, not only is it extremely difficult and costly to manufacture a multilayered ceramic feed-through, but the process of brazing the ceramic feed-through to the metal package such that it is hermetically sealed has a low yield rate, and thus there are limitations to reducing the cost of the optical module.
Furthermore, in conventional technologies, a high price ceramic submount is used to transmit and process a high frequency signal in an optical transceiver module of a data rate of 10 Gbps or more, and in the ceramic submount and FPCB, CPW (CoPlanar Waveguide) type electrodes are used. Herein, in order to transmit the high frequency signal without any reflection, a termination matching resistor is integrated onto the ceramic submount in a thin-film type, and in order to prevent the high frequency signal from being distorted by resonance, a ground via hole that electrically connects an upper ground and a lower ground is formed. Forming such a thin-film type matching resistor and forming the ground via hole on the ceramic submount are very expensive processes, which would account for a significant portion of the cost of subsidiary materials.
Not only that, when using the ceramic feed-through, in the optical module, the ceramic submount and the ceramic feed-through are connected by wire bonding to transmit an RF signal, and in the outside of the optical module, the FPCB is connected to the ceramic feed-through by soldering to transmit an RF signal. When using such different bonding methods, that is, wire bonding and soldering, for each part of the ceramic feed-through, there is a problem that reflection may increase due to the mismatch of characteristic impedance when transmitting an RF signal, causing signal distortion.